This research program focuses on the general hypothesis that developmental changes in selected peptides, including the uniquely mammalian hormone oxytocin (OT), may have long lasting effects on mammalian development. The purpose of these projects is the experimental analysis of the more specific hypothesis that postnatal manipulations of OT may influence the subsequent development of various endocrine and behavioral systems. Two animal models (domestic rats and prairie voles) will be subjects in these experiments. Experiments will be designed to examine the consequences of acute and repeated developmental manipulations of OT during the neonatal period. We propose to focus on neuroendocrine and behavioral functions of OT, including effects on reproductive and social behaviors the HPA axis. The specific dependent variables to be examined were selected because each of these functions has been shown to be sensitive to OT in adulthood. Several of the functions of OT are especially apparent in females. Therefore, to marrow the scope of these studies, we will focus initially on female behavior and endocrinology.